Jointed-arm robots can perform complex actions because the various sections of the jointed arm turn around six joints or axes. A jointed-arm robot such as the industrial robot 10 shown in FIG. 1 has a base 13, a shoulder 14, an elbow 15, an arm 16, a wrist 17, and an end effector 18. The end effector of the robot is one of its more important components because it allows the robot to grip or hold objects of interest.
Various robot end effectors or grippers are known in the art. For example, U.S. Pat. No. 5,163,729 (the "'729 Patent") discloses a parallel gripper having a main body made from a solid block of material. The main body has four relatively long bores and two chambers or cylinders formed within it. Each chamber or cylinder formed in the main body has a piston within it, the piston connected to a piston rod. A pair of opposed jaws are supported with respect to the main body by two pairs of support or guide rods. Each guide rod is slidably received in one of the four bores. The guide rods support the jaws for movement toward and away from the main body. The movement of each mounting block is effected by one of the two cylinder-piston assemblies in the main body. One of the guide rods supporting each of the mounting blocks is provided with a pinion rack which is disposed in meshing relationship with a pinion gear. The interaction of the guide rods, one coupled to each mounting block, via the pinion gear, causes the movement of the mounting blocks to be synchronized when the pistons in the cylinders are activated.
A similar device is shown in U.S. Pat. No. 4,591,199 (the "'199 Patent"). The '199 Patent discloses a gripper having two coaxial fluid chambers. Each chamber has a piston that moves within it and each piston is connected to a jaw. Movement of the pistons toward and away from each other causes the jaws to move toward and away from each other. Each piston is mounted to one end of a threaded rod. The rod is mounted in a bearing and is used to synchronize the motion of the two jaws.
While the devices shown in the '729 and '199 Patents are acceptable for some applications, they have several drawbacks. First, the synchronizing mechanisms in each device have interacting teeth and grooves. In the '729 Patent the teeth on a pinion gear mesh with the teeth on a pinion rack. In the '199 Patent, the female threads in the piston are engaged with male threads in the rod. These types of mechanisms must be lubricated to operate properly and can, under certain conditions (e.g., insufficient lubrication or misalignment of teeth), bind or jam, causing the gripper to malfunction. Second, each of the devices has a solid or closed body design. Specifically, each of the devices is constructed in such a way that the cylinders or chambers that hold the pistons are surrounded by thick walls. These walls are used as weight bearing members in each gripper and are directly exposed to the operating environment of the grippers.
The drawbacks of grippers or end effectors like those shown in the '729 and '199 Patents are particularly apparent when they are used to handle relatively high volumes of objects, relatively hot objects, or both. With respect to high temperature applications such as removing an aluminum wheel from a furnace, heat may be transferred directly from the wheel and ambient air to the end effector. This heat may affect the components of the end effector and, in particular, affect the cylinder seals. Excess heat in the cylinder seals can cause excess wear and binding of the cylinder-piston assembly. Efforts to mount heat shields externally on end effectors have proven less than satisfactory. While the shields prevent over heating, they often cause weight and balance problems for robots.
With respect to high volume applications, maintenance, lubrication, and binding problems are more prevalent when large numbers of objects are handled. To handle each object, the jaws of the end effector must be opened and closed or cycled at least once. The probability of a lubricant failure or misalignment of the teeth in a synchronizing mechanism increases the more times the jaws are opened and closed. Thus, there are typically more binding and jamming problems in existing end effectors when a large number of objects are handled.
Accordingly, there is a need for an end effector that can be used in relatively high temperature, high volume applications without overheating or jamming. Further, it would be desirable if such an end effector had a relatively simple design and could be constructed from commercially available components.